Many ideas for improvements in the world's energy usage focus on increasing the efficiency of existing types of engines. Most heat engines are limited in their efficiency by the theoretical efficiency of the Carnot cycle, which requires an increase in operating temperature in order to increase operating efficiency. Rather than the focus on efficiency, it may be desirable to harvest energy at a reasonable efficiency from relatively slight differences in temperature between two volumes. Currently, electric energy is typically produced by boiling water and using the steam generated to drive a turbine. This works very well if one creates a first volume with a temperature above the boiling point of water and a second volume with a temperature below the boiling point of water.
If, however, one wishes to harvest a temperature difference between two volumes, both of which are at a temperature below the boiling point of water, this method is unavailable. Although there are liquids, other than water that have different boiling points, there is far from a complete and convenient mapping of temperature differences to liquid boiling points. Accordingly, additional methods of harvesting energy from temperature differentials are desirable.
Additionally, although thermal engines employing a solid phase change material, such as Nitinol, have been designed, these engines tend to be rather inefficient and do not take advantage of the full phase change expansion that Nitinol undergoes. Many of the existing designs do not fully insulate the heat source from the heat sink and therefore do not efficiently use the available heat. Accordingly, there is a need for a more efficient engine that utilizes a phase change material.